Hydrography^ and the Art of Navigation. 61 



compensation, are, it is true, completely wanting. In the ab- 

 sence of these, a new form will be immediately given to the ar- 

 gument, and it will be said (which is in reaHty the case), that in 

 summer, at equal latitudes, the waters of the Mediterranean are 

 from 3^ to 3°5 Cent, (about 6° Fahr.) warmer than those of the 

 oceaD, from which it inevitably follows that the first undergo 

 more evaporation than the others, and that nothing more is re- 

 quired to explain the current of the strait. 



And this, it must be confessed, would be sufficient, if the 

 cause indicated were to produce a very sensible difference of level 

 in the two seas. Thus, whatever may have been said of it, the 

 problem will be found to be reduced to one of numbers, or to a 

 question of facts. It 'must be found out, either by calculation 

 or experiment, to what extent the Atlantic Ocean is higher than 

 the Mediterranean. The calculation, I have already stated, 

 will be difficult to be made with precision, owing to the want of 

 sufficient data. With regard to the experiment, the results of 

 that which I am about to present, seem to me calculated to sa- 

 tisfy the most scrupulous minds. 



Delambre found the direct means of inquiring into the com- 

 parative level of the two seas, by the great chain of triangles 

 on the meridian of France, which extended from Dunkirk 

 as far as Barcelona. The triangles comprehended between 

 Rhodes and the Mediterranean, affiarded him for the vertical 

 height of that town, a result which agreed to a fraction of a 

 metre with the height of the ocean, as deduced from that por- 

 tion of the chain placed between Rhodes and Dunkirk. 



It has been stated in opposition to this view, that the obser- 

 vations from which it was deduced, were not always made in 

 favourable circumstances; that it is necessary they should be 

 frequently repeated before they could be assumed as proving a 

 difference of level; and that, moreover, the calculations had 

 neither been made with sufficient care, nor on a plan sufficiently 

 accurate. These objections are not without weight. The offi- 

 cers of the body of geographical engineers have likewise endea- 

 voured to take advantage of the chains of triangles of the first 

 order, drawn in different directions, which cover the whole sur- 

 face of France, to submit the question of the respective levels 

 of the two seas to a new examination. M. Delcros, among 



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